The present invention relates to ball valves used to control the flow of fluids, and is more particularly concerned with a novel ball configuration which exerts a reduced force against the valve seats when the ball is in its open position in the valve, thereby increasing the life of the seats used in such valves.
Ball valves are in themselves well known in the art, and commonly comprise a housing or valve body having an interior cavity located between and communicating with a pair of fluid flow channels to define an axial flow passage extending through the housing. A ball is located in the cavity and is provided with an axially directed bore extending therethrough which car be selectively aligned with, or disposed transverse to, the axial flow passage in the housing by rotation of the ball through, e.g., 90.degree., thereby to control the flow of fluid through the axial flow passage. A pair of annular seat rings are supported by the housing in surrounding relation to the axial flow passage adjacent the upstream and downstream sides of the housing cavity, the seats being in sealing engagement with both the housing and the ball.
In valve arrangements of the aforementioned type seat life has been a problem. Since the ball is normally in sealing engagement with the seats in both the open and closed position of the ball, the seats tend to wear out after a period of time and must be replaced. The problem is particularly pronounced when the valve is used to control the flow of an abrasive fluid and/or when the fluid being controlled has a comparatively high pressure and/or when the valve is used under service conditions which require that the valve be rapidly cycled between open and closed valve positions. To a lesser degree the same problem is present in all fluid flow applications of ball valves. When a seat has become worn or is otherwise no longer capable of performing its intended sealing function, the seat must be replaced to eliminate consequent leakage of fluid through the closed valve. Such seat replacement requires that the valve taken out of service temporarily and, in addition, gives rise to the costs attendant the provision of new seats and associated repair of the valve.
In an effort to deal with the foregoing problem, valve arrangements have been suggested heretofore which reduce seat loading when the valve is in its open position. For example Pryor U.S. Pat. No. 3,064,937 discloses a ball valve which utilizes a permanently split ball consisting of two ball halves that are slidable relative to one another, and associated cam plates cause the ball halves to be forced into the valve seats as the ball is rotated to the valve closed position, and to be moved away from the seats as the ball is rotated to the valve open position. A somewhat analogous arrangement is shown in Sivyer U.S. Pat. No. 3,124,333 wherein a cam, which rides in a split at the bottom of the ball, spreads the ball to form a tighter seal with the valve seats as the ball is rotated to its closed position. Other arrangements utilize plug segments which cooperate with a single seat in the valve, and which are mounted eccentrically on an actuator shaft so that the plug segment is moved into forcible engagement with the associated seat in the closed position of the valve, and moved away from the seat as the segment is moved to the valve open position. Arrangements of this type are shown for example in Zeigler et al U.S. Pat. No. 3,191,906, Pfundstein et al U.S. Pat. No. 3,809,361, Rihm et al U.S. Pat. No. 4,073,473 and Myers U.S. Pat. No. 4,118,008. Rotary valves employing split or axially movable balls are, however, comparatively complicated and expensive to manufacture and maintain. Eccentrically mounted plug segments suffer from the disadvantages that, since they involve an asymmetrical or unbalanced design, they are prone to problems arising from tolerance variations, are not self centering, and are position sensitive rotationally.
The present invention is intended to obviate all of these problems by the provision of a ball of novel configuration which is symmetrical in shape, balanced in design, and so configured that, as the ball is rotated in a substantially conventional valve housing from its open position to its closed position, the ball surface gradually seats on a pair of associated upstream and downstream valve seats to achieve maximum seat loading at the full closed position of ball rotation.